Field of the Invention
The present invention relates to a light emitting diode (LED) package. More particularly, the present invention relates to a backlight unit including an LED package and a liquid crystal display device including the backlight unit.
Discussion of the Related Art
An LED package where an LED is mounted on a frame has been used as a light source of a lighting apparatus and a liquid crystal display (LCD) device.
In general, the LED of the LED package includes a semiconductor having a positive-negative (pn) junction of a p-type semiconductor material and an n-type semiconductor material. A wavelength of a light emitted from the LED may be adjusted according to a kind of a compound for the semiconductor.
Since the LED has a low power consumption and a small size as compared with another light source, the LED may be suitable for the LCD device. The LED emitting a white light has been used for a conventional LED package of the LCD device. For example, the LED package (e.g., Patent Document 1: Japanese Publication No. 2014-154644) including a plurality of LEDs emitting different colored lights and the LED package (e.g., Patent Document 2: Japanese Publication No. 2007-067184) including an LED and a fluorescent material combined to the LED may be used.
As an organic light emitting diode (OLED) display device is put to practical use, a color reproducibility of the LCD device becomes crucial. A color display of the LCD device is obtained by absorbing a light of a partial wavelength band from a light emitted from a white colored light source with a color filter. For the purpose of improving the color reproducibility of the LCD device, it is effective to decrease the wavelength band of the light passing through the color filter. However, when the wavelength band of the light passing through the color filter decreases, a problem such that utilization efficiency of the light is reduced occurs. To solve the above problem, it is required that the light source emits a light having a narrow wavelength bands corresponding to three primary colors of light and the wavelength bands of light passing through the color filter is matched with the wavelength bands of the light emitted from the light source.
Accordingly, a quantum dot (QD) has been used as a fluorescent material combined to the LED (e.g., Patent Document 3: Japanese Publication No. 2012-191144)
The quantum dot uses light from the LED as an excitation source and emits light with a longer wavelength than that of the excitation source. In addition, the wavelength of the light emitted from the quantum dot can be controlled by changing the type and the size of the quantum dot. Moreover, the quantum dot has high quantum efficiency approaching that of YAG (yttrium aluminum garnet) fluorescent material. Therefore, it is possible to obtain an LED package having desired emission color, high brightness and emission spectrum with a narrow full width at half maximum (FWHM) by using the quantum dot. Furthermore, it is possible to manufacture an LCD device having wide color gamut by using an LED package of the quantum dot as a light source of the backlight unit.
However, there is a problem that the quantum dot is degraded in a short time when it receives a light from the LED in the presence of moisture and oxygen. Additionally, when the quantum dot is disposed adjacent to the LED of the excitation source, the degradation of the quantum dot is accelerated in circumstances of large amount of light and high temperature.